How paternity testing is like international trade

Nonpaternity rate % N
Switzerland 0.83 1607
USA, Michigan, white 1.49 1417
USA, California, white 2.1 6960
USA, Hawaii 2.3 2839
UK, West London 3.7 2596
Paternity Testing Laboratories
UK 16.6 1702
USA, Los Angeles, white 24.9 1393
Sweden 38.7 5018
South Africa, Cape Coloured 40 1156

The results above are from Kermyt Anderson’s How Well Does Paternity Confidence Match Actual Paternity? This is still one of the best surveys of the field, despite being 12 years ago. A more recent paper, Cuckolded Fathers Rare in Human Populations, uses more powerful genetic genealogy methods to come to the same conclusion as Anderson’s survey: extrapair paternity, or nonpaternity events, are rare in Western societies. I don’t think it is limited to Western societies. I suspect that when high throughput sequencing is applied to Chinese clan lineages and Hindu gotras, you will found that nonpaternity events are similar to those in the West.*

On the other hand, in some small-scale societies, the rates are much higher.

I won’t delve into the evolutionary anthropology here. Rather, I want to point to a new paper, Growth of ancestry DNA testing risks huge increase in paternity issues. Ancestry testing is huge. Within the next year, it is almost certain that 10% of the American population when having some sort of high-density genomic testing done.

As the author of the paper pointed out to me on Twitter, 1% of 16 million people is still a lot. Yes, in absolute terms. But we need to look at the other side of the equation.

In Anderson’s original data one of the interesting results is that in most datasets drawn from paternity testing laboratories, where there is a very high suspicion of nonpaternity events, most of the fathers nevertheless were biological fathers! In a nonpaternity testing context, nonpaternity events will be much closer to ~1%. But, I think it is reasonable to suppose that some of the 99% of the fathers who turn out to be biological fathers also have suspicions…which are unfounded.

Like free trade, you tend to see one side of the equation much more than the other. In free trade scenarios, a minority of workers may lose their jobs or have to work under reduced wages, but the vast majority of consumers will get cheaper or better products. The former is much more salient than the latter.

Similarly, the small minority of fathers and families who are going to be “surprised” in a negative way, is balanced out by the likely larger number who have low-grade suspicions, but in fact, are confirmed in their biological relatedness.

Addendum: Needless to say, if you are part of the “cuckold community”, you should probably not getting this sort of testing.

* The necessity of good quality whole-genome sequencing is due to the fact that male relatives are excellent candidates for nonpaternity events. To get a certain estimate one would want to count unique mutations across the pedigree.